1. Technical Field
The present invention generally relates to a metallic catalyst carrier used in a catalytic converter for cleaning exhaust gas. More specifically, the present invention relates to a metallic catalyst carrier comprising a flat sheet and a corrugated sheet that are made of metal and laminated together.
2. Description of Related Art
A catalytic converter is used for cleaning exhaust gas. The catalytic converter has an outer casing with a metallic catalyst carrier located therein. The metallic catalyst carrier can be made by stacking and then rolling a corrugated metal sheet and a flat metal sheet together, such as described in Japanese Laid-Open Patent Publication No. 6-312141 is known. This metallic catalyst carrier is divided into a front part and a rear part with the boundary therebetween existing at the slits formed in the corrugated sheet and the flat sheet. The slits formed in the corrugated sheet and the flat sheet extend in the rolling direction of the corrugated sheet and the flat sheet. The front part and the rear part are formed as a result of these slits being formed in mutually corresponding positions. Also, between the front part and the rear part, there exists a connecting part that is a slight portion remaining from the formation of the slits. Thus, the front part and rear part are not completely separated. Rather, the front part and rear part maintain a connected condition via the connecting part. Furthermore, the fragile connecting part is plastically deformed by twisting the front part and the rear part in the circumferential direction with respect to each other. Consequently, a misalignment is formed between the cell passage inside the front part and the cell passage inside the rear part. As a result, exhaust gas that has passed through the front part creates turbulence at the slit area when it flows into the rear part. In this manner, the exhaust gas cleaning performance is improved.
Another type of metallic catalyst carrier is described in Japanese Laid-Open Utility Model Publication No. 6-29621. This type of metallic catalyst carrier comprises a corrugated sheet and a flat sheet rolled together, so as to form a front part, a middle part, and a rear part in the exhaust gas flow direction. Space parts are formed between the front part and middle part, and between the middle part and rear part, respectively. These space parts are constructed by forming two slits in the corrugated sheet and the flat sheet so as to extend in the rolling direction of the corrugated sheet and the flat sheet. The two slits are formed on a portion other than the portion constituting the outermost circumferential part of the carrier, such that the front part, middle part, and rear part are integrated into a single metallic catalyst carrier.
In view of the above, there exists a need for an improved metallic catalyst carrier that effectively improves the exhaust gas cleaning performance. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that an effective way to improve the exhaust gas cleaning performance is to actively cause turbulence of the exhaust gas passing through the inside of the metallic catalyst carrier. This also increases the chances for the exhaust gas to contact the catalyst. However, in the metallic catalyst carriers previously explained, improvement of the exhaust gas cleaning performance by means of turbulence can only be achieved at the slit portion formed between the front part and the rear part. Consequently, one must widen the slit width or increase the number of slits if one wishes to further improve the exhaust gas cleaning performance.
However, increasing the number of slits means providing many slits that extend in the rolling direction of the corrugated sheet and the flat sheet, and having a carrier structure with multiple parts. Consequently, there is the possibility that warping and cracking will occur during corrugation processing of the corrugated metal sheet, the rolling of the flat sheet and the corrugated sheet together, or twisting of various portions of the carrier in order to cause turbulence. Furthermore, since turbulence is caused by twisting, the carrier in the circumferential direction in front of and behind the slits, improving the exhaust gas cleaning performance by increasing the number of slits will increase the number of times each part is twisted. Therefore, productivity of producing such a metallic catalyst carrier is worsened.
Also, if one attempts to improve the exhaust gas cleaning performance by widening the slit width to strengthen the turbulence of the exhaust gas, the open area ratio of the carrier will be increased and the cleaning performance can be improved. However, when, for example, high pressure exhaust gas passes through suddenly, there is the possibility that buckling will occur due to the connecting parts that cross the slits not being strong enough to be withstand the pressure of the exhaust gas.
Meanwhile, in the latter of the metallic catalyst carriers previously explained, the width of the portions constituting the carrier will be narrowed if many space parts, where turbulence forms, are formed by increasing the number of slits without changing the overall length of the carrier in the exhaust gas flow direction. Consequently, the width of the weld between the corrugated sheet and the flat sheet is narrowed. Accordingly, there is the possibility that the weld portion will come apart under the pressure of high-pressure exhaust gas.
The present invention was conceived in view of these above-mentioned issues. In order to achieve the aforementioned objectives, a metallic catalyst carrier is provided with a flat metal sheet; and a corrugated metal sheet laminated to the flat metal sheet to form a plurality of cell passages that extend longitudinally between the flat metal sheet and the corrugated metal sheet such that exhaust gas passes in a longitudinal direction through the cell passages. One of the flat metal sheet and the corrugated metal sheet has a plurality of elongated holes. Each of the elongated holes has a length being aligned in a lengthwise direction to form a plurality of hole lines arranged in a direction that intersects with the longitudinal directions of the cell passages. The elongated holes in each of the hole lines are separated by a prescribed distance in a direction substantially perpendicular to the longitudinal directions of the cell passages.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.